96 Cincinnati Society of Ifafural History. 



disk provided with a large number of outwardly directed, short and 

 slender spines. Oral pieces ten, sub-rhomboidal in outline, arranged 

 in pairs, each pair being formed of two of the marginal series of ray 

 plates ; on the lower inner edge there are five spines, and extending 

 from each pair, over the mouth, is a bundle of rather long ones. 



Rays apparently very flexible, contracted towards the mouth ; six 

 series of plates are exposed on the ventral side of each ray. The two 

 middle series alternate regularly, and interlock along the mesial line; 

 they are about twice as long in the direction of the ray, than measur- 

 ing transversely; each piece is contracted in the middle on the inner 

 side to admit the wide ends of the two pieces immediately opposite, and 

 on the outer side to form a pore like impression, between them and the 

 outer series of plates; four of these plates in each range of each ray 

 are included within the disk, and the series terminate abruptly at a dis- 

 tance of one and a half lines from the inner end of the oral plates; from 

 the margin of the disk to the extremity of the ray there are about six- 

 teen pieces in each range. The pores mentioned above, are occupied by 

 a series of loosely fitting, obtusel^^ conical or pyramidal plates, some of 

 which distinctly show a deep depression in the top, and may have been 

 perforated. Outer or marginal pieces flat, placed on edge, and directed 

 obliquely outward so as to overlap each other; the two free edges, /. e., 

 the one toward the point of the ra3^s, and the one seen on the A^entral 

 surface, are lined with from ten to twelve short club-shaped spines, 

 varying somewhat in length. The marginal and middle series of plates, 

 articulate by means of corresponding prolongations from the sides of 

 the plates. These prolongations arise from near that end of the plate 

 which is directed towards the mouth. 



Dorsal side of rays composed of two rows of alternating and inter- 

 locking plates, which near the disk are wQvy deepl}^ sculptured, and 

 about as wide as long, becoming gradually less excavated, and longer 

 in proportion to the width, toward the point of the raj^s; on each side 

 they articulate with the upper edge of the oblique marginal series of 

 plates. 



Breadth of disk, .60 inch; breadth of arm at margin of disk, .16 inch; 

 length of same from oral plates, .88 inch. This species is related to 

 Protaster flexuosus. of Miller and D\^er, described in the first num- 

 ber of this Journal. 



Locality and Position. — The specimens examined are in the cabinet 

 of the author, and were found by him at an elcvatioh of 100 ft. above 

 low water mark in the Ohio river, at Covington, K}'. 



DISCINID^. 

 Genus Discina. 

 DisoiNA TENuisTiMATA, u. sp. (Plate IV., fig. 10.) 

 'Shell under medium size, thin and circular, 



